Tran Hiep, a 50-year-old Australian-Vietnamese democracy campaigner, was due to return to Bangkok, Thailand, to reunite with his wife Chloe Dang after a short trip to Phnom Penh, Cambodia, to meet with human rights defenders.
But he never boarded his flight and has not communicated with his wife since September 18, leaving her worried for his safety.
"My family and I are really worried about his safety, and we just only want to know where he is and what happened to him," Ms Dang told AAP from Bangkok airport before boarding a flight to Melbourne.
"My husband deserves protection, and I really hope the Australian government will continue to put pressure on Cambodia to do an investigation to find out where he is right now."
Mr Hiep, a freelance IT professional who founded the Australian Alliance to Combat Human Trafficking, was travelling with another human rights activist Nguyen Duc Thuan, who is also Vietnamese and holds a Norwegian passport.
The pair travelled to Cambodia to meet with dissident Vietnamese activists for training.
Vietnam in recent years has ramped up its crackdown on dissidents, with more than 55 activists arrested under broad criminal laws in 2025.
Civil society groups and United Nations human rights experts have repeatedly warned of growing co-operation between Vietnamese authorities and neighbouring governments targeting advocates.
Viet Tan, a pro-democracy diaspora political party, has described the pair's disappearance as concerning given previous cases involving Vietnamese dissidents vanishing in neighbouring countries and subsequently appearing in custody in Vietnam.
"Their disappearance is not an ordinary 'missing person' incident. Both men are long-time human rights advocates and Viet Tan members," the organisation said.
Ms Dang, 36, said fretting over her husband's whereabouts had taken a psychological toll.
"It's been 11 days and I'm really in the dark," she said, choking back tears.
"I don't know where he is and how he's doing - it's driving me crazy.
"Everything is really uncertain."
The Australian government confirmed consular officials were in contact with Ms Dang but declined to comment further.
"The Department of Foreign Affairs and Trade is providing consular assistance to the family of an Australian reported missing in Cambodia," a department spokesperson told AAP on Monday.
The families of the missing men have filed an appeal with the UN Working Group on Enforced or Involuntary Disappearances.
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